1. Field of the Invention
The invention relates to a method of producing an electrode for an electricity storage device.
2. Description of Related Art
Electricity storage devices, as typified by lithium ion secondary batteries, electric double-layer capacitors, and their combinations (the lithium ion capacitor is a typical example) have become increasingly important in recent years. In particular, the lithium ion secondary battery, which provides a high energy density at a low weight, is preferentially used as a high-output power source for installation in vehicles. In a typical lithium secondary battery structure, electrodes are provided in which an electroconductive member (current collector) carries an electrode active material layer that contains an electrode active material capable of reversibly incorporating and discharging the lithium ion, which functions as the charge carrier. In a typical structure for an electric double-layer capacitor, electrodes (polarizable electrodes) are provided in which an electrode layer including a polarization material (also called “active material”) on an electroconductive member (current collector), such as active carbon. The polarization material is capable of forming ion and charge layers (the electric double layer) by adsorbing cations or anions. These electrodes are typically produced by: first dispersing a solids fraction material, i.e., the electrode active material (here and below this includes the polarization material referenced above), a conductive material that exhibits a high electroconductivity, a binder, and so forth, in a suitable solvent to produce a paste-form composition (this composition is referred to simply as a “paste” in the following) to form the electrode active material layer; coating this paste in layers on the surface of a current collector; and then drying this applied paste to remove the solvent and form an electrode active material layer including the electrode active material on the current collector. The paste-form includes slurry-form and ink-form.
There have been numerous attempts with regard to the production of these electricity storage device electrodes to improve the properties of the obtained electrodes and electricity storage devices by controlling the state of the electrode active material present in the paste to form the electrode active material layer. For example, WO 2001/092158 discloses that—by using a specific chemical composition for a lithium-transition metal complex oxide that is the positive electrode active material for a lithium ion secondary battery, and by bringing the curve gradient in the cumulative volume-particle size distribution curve at a 20% cumulative volume percentage and the curve gradient at an 80% cumulative volume percentage into prescribed ranges—the compressive flow of the particles during pressing can be facilitated when electrode production is carried out using particles of this lithium-transition metal complex oxide. Thus, a high-capacity electrode can be produced.
However, the improvements in the state of the electrode material, e.g., the active material particles, as referenced above have been carried out with the objective of improving electrode performance. That is, there have been no efforts at actively modifying and/or controlling the state of the electrode material with the objective of improving the production method rather than the electrode (the production target).